A true LIP particle is one that interacts only gravitationally. Examples of true LIPs are primordial black holes. Such particles, in order to make up the dark matter, must be stable against Hawking radiation [1]} up until the present epoch. Thus their mass must be greater than \(10^{15}\)  g. Astrophysical constraints on such primordial black holes are discussed in Ref. [2]} and [3]}.
